Warning indicated 85 km/h, wind was 120. How to protect yourself from a storm that grows from heat

Slovakia experienced a storm on Thursday evening that one cannot get used to. In the morning, warnings were in effect for heat waves and temperatures in the south were rising toward 34 degrees, in the evening a supercell swept through Bratislava and a station near Nitra measured wind gusts of 119 kilometers per hour. The original warning, however, spoke of wind gusts of 65 to 85 kilometers per hour. This article is not about what happened, but about what to do with such a storm next time.Read also: A storm with hail and power outages swept through Bratislava. A meteorologist speaks of a supercell

Hot and humid air is storm fuel, not its opposite

The surprise that a destructive storm comes after a hot day is understandable, but meteorologically it is the other way around. Hot and humid air at ground level is precisely the energy reserve from which a strong storm forms. The overheated earth's surface pushes warm air upward, at altitude it cools, water vapor condenses and in doing so releases so-called latent heat, which further accelerates the rising current. The hotter and more humid the air at ground level, the greater the energy the storm has at its disposal. Povetrie.sk ↗

Heat alone, however, is not enough. A trigger must come, most often a cold front or wind convergence at ground level, and suitable atmospheric layering. This is precisely why such a storm can be unpleasantly sudden. Meteorologists can predict in advance that conditions for strong storms will be favorable, but not exactly where and at what time they will form. Povetrie.sk ↗

This yields a practical conclusion for the reader. If it is a hot day and the forecast mentions storms, there is no point waiting for something to appear in the sky. Planning must be done in the morning. By evening, moving from an exposed location may already be too late.

First level does not mean weak storm

This is probably the most common misunderstanding. A first-degree warning does not mean a weak phenomenon; it means a phenomenon that can occur several times a year. SHMÚ defines it as a phenomenon that can cause relatively small danger and smaller-scale property damage. A second level is a phenomenon that is not common and can threaten human activity, a third seriously threatens human activities. SHMÚ ↗

The level thus speaks to the expected degree of danger and how often such a phenomenon occurs, not whether it will harm you specifically. On Thursday, the first-degree warning had parameters of a heavy downpour of 20 to 30 millimeters in half an hour and wind gusts of 65 to 85 kilometers per hour. ta3 ↗

The measured values were substantially higher and SHMÚ raised warnings to the second level for six regions during the evening. In itself, this does not necessarily mean a forecast failure. A warning covers the entire district for several hours, while the strongest wind in such a system concentrates into a narrow band and a short moment. That is why it is worth reading the text of the warning, not just its color. Refresher ↗

What to do while the storm is still far away

Most of the damage that can be prevented is prevented before the storm, not during it. The Ministry of Interior and the Office of Public Health recommend securing loose objects on balconies, terraces and in gardens, i.e. umbrellas, furniture, trampolines and clotheslines. Wind can move them suddenly and what flies away becomes a projectile. Office of Public Health of the SR on SHMÚ website ↗

Do not park your car under trees, near scaffolding, billboards or electrical lines. On Thursday in Bratislava, a billboard near Aupark fell, scaffolding collapsed elsewhere, and in Petržalka trees buried parked cars. Aktuality.sk ↗

Further, there are several small things that take a few minutes. Close windows and skylights, bring pets inside, unplug sensitive appliances from the socket before the storm arrives, and charge your phone, as power outages are associated with this type of storm. If you are planning a hike or a trip to water, reschedule it. Bratislava City Forests on Thursday directly urged people to postpone their visit to the forest park. TASR ↗

When the storm is above you

If you hear thunder, lightning is already close enough to endanger you. There is no need to wait for rain, because lightning can strike even where it is not yet raining. The goal is a solid enclosed building or a car with a solid metal roof and closed windows. Protection there is not provided by tires, but by the conductive body. SITA ↗

A safe shelter is not a tent, a gazebo, a pergola, an open shelter, a bus stop or an umbrella. These protect from rain, not from lightning. Similarly, a bicycle or motorcycle does not provide protection. SITA ↗

Rules apply even in an apartment. The Office of Public Health recommends staying away from windows and glass surfaces, not touching running water and water pipes, and not using devices plugged into an outlet. A mobile phone without a charger is fine, a telephone on a landline is not. Office of Public Health of the SR on SHMÚ website ↗

In the terrain, you must stay away from peaks and ridges, isolated trees, poles, metal fences and railings, and descend to lower ground. During hail, protect your head with a backpack, bag or at least your hands. If you are in a group, do not stand crowded together; a distance of at least three meters reduces the risk that one discharge will strike several at once. Office of Public Health of the SR on SHMÚ website ↗

Where Slovak and American recommendations diverge

At one point, official advice differs and it is worth knowing about it. The Office of Public Health of the SR for a situation in the open recommends seeking a depression, assuming a crouched position with feet together, i.e., a variant of the so-called storm crouch. Office of Public Health of the SR on SHMÚ website ↗

The American meteorological service NWS stopped recommending this procedure in 2008. It argues that the crouch does not provide substantial protection and that promoting it creates a false sense of safety, that is, that there is a correct position that will save a person. Instead, it emphasizes that a person should not get into such a situation at all. NWS ↗

The difference is smaller than it seems, and in practice can be summed up simply. Both sides agree that no place under the open sky is safe and that the only real solution is a solid building or car. If shelter is no longer within reach, body position is the last and weak insurance, not a plan. Do not waste time looking for the correct position and continue to shelter.

Lightning is not the only risk

Storms attract most attention to lightning, but on Thursday the damage was caused primarily by wind and water. The Office of Public Health mentions breaking branches and uprooting trees, collapsed roofs, scaffolding, fences and billboards, flying unsecured objects and fallen electrical lines. This list was filled almost point by point on Thursday. Office of Public Health of the SR on SHMÚ website ↗

A second underestimated threat is water. SHMÚ warns of flooding of underpasses, passages and roads during heavy rains. The rule is simple and merciless; do not enter a flooded underpass. A car in it can be flooded or swept away by the current, and you never know in advance how deep the water under the surface is. Refresher ↗

The basic rule of the Office of Public Health is to move strictly outside the flooded area. Never enter flowing water. If you cannot tell if water is flowing, do not approach it and go around it instead. The Office of Public Health allows testing by throwing a piece of wood, but only from a safe distance. Still water is not safe either; it is usually polluted and there may be glass, nails or an open sewer under the surface. Do not touch downed electrical lines and keep your distance from them. Office of Public Health of the SR on SHMÚ website ↗

If a vehicle begins to flood, leave it if it can be done safely and move to higher ground. If a tree falls on it, first consider whether there is a threat from electrical cables, further falling branches or passing vehicles. In case of injury or being stuck, call 112. A person struck by lightning can be safely held; his body does not remain charged, and help should be called immediately at 112 or 155 and resuscitation should begin if he is not breathing normally. Medical examination is also needed for anyone who is conscious after an impact. TASR/Refresher ↗

After the storm, wait at least 30 minutes after the last thunder before going back outside. Lightning appears on the back of the storm too, and weakening rain does not yet mean the end. If it thunders again during the wait, start counting from the beginning. SITA ↗

What hotinfo is watching

Whether SHMÚ will clarify its communication of warning levels after this episode, given that the difference between the announced 85 and measured 119 kilometers per hour was large.

The balance of interventions by the Fire and Rescue Corps on Thursday evening and how many of them were related to trees falling on cars and roads.

Whether the recommendation of the Office of Public Health of the SR on body position in the open will be aligned with the practice of the American NWS, which abandoned storm crouch seventeen years ago.

How often such episodes will come at the end of heat waves, which is an issue SHMÚ is monitoring as part of assessing climate extremes.

Illustration photo: a storm line with shelf cloud over Varbla in Estonia. Author Kristian Pikner, Wikimedia Commons, license CC BY-SA 4.0.